The present invention relates to an exhaust gas turbocharger and, more particularly, to an exhaust gas turbocharger for an internal-combustion engine in which the turbine drives a compressor and has an adjusting mechanism for influencing the turbine flow conditions such that a blow-off device and the adjusting mechanism can be actuated by a single actuator.
It is generally known to control the performance of the turbine of an exhaust gas turbocharger in order to achieve a favorable course of the torque in a wide rotational speed range of an internal-combustion engine. The limits of the performance control are set by, among other things, the relationship between the maximal and the minimal turbine mass flow, the so-called absorption capacity The control is primarily possible only by an adaptation of the absorption capacity because, in the case of an existing internal-combustion engine, the exhaust gas mass flow is established by the working volume and the rotational speed. If the exhaust gas offered by the internal-combustion engine rises above a maximally permissible turbine mass flow, the performance of the turbocharger compressor will rise and thus the charge pressure will rise. In order to avoid any resulting damage to the internal-combustion engine, it is known to lower the overall efficiency of the turbocharger by not making a part of the exhaust gas quantity available to the turbine wheel.
In the German Patent DE 35 07 095 C2, a charge pressure control arrangement of an exhaust gas turbocharger is disclosed in which a throttle valve arranged in front of the turbine inlet controls the turbine performance, and a blow-off valve guides a portion of the exhaust gase past the turbine if the rotational speed of the engine continues to increase. The throttle valve and the blow-off valve are actuated by one actuator respectively. The actuators are controlled by a control device on the basis of the rotational speed of the engine and supplied intake air. The entire charge pressure control therefore requires high expenditures and the coordination of the two actuators with respect to one another presents problems.
German Patent DE-OS 35 31 296 shows a control arrangement having a turbocharger with a variable performance in which blades in front of the turbine wheel inlet can be adjusted into four different positions for the control of the charge pressure. The adjustment takes place by way of compressed air as a function of the power and the rotational speed of the engine. The disadvantage of this control arrangement is the non-continuous adjusting of the blades in four steps and the high mechanical expenditures of the blade adjusting arrangement.
It is an object of the present invention to provide an exhaust gas turbocharger which, in a wide rotational speed range of an internal-combustion engine, permits an adaptation to the compressor performance required for a desired charge pressure and is constructed in a manner that is as simple as possible.
According to the invention, this object is achieved by actuating the adjusting mechanism and a blow-off device which guides a portion of the exhaust gases past the turbine by a single common actuator.
The exhaust gas turbocharger according to the present invention makes it possible with a single actuator to continuously actuate the guide blades at the turbine inlet and thus control the charge pressure over a wide rotational speed range, as well as to actuate a blow-off device integrated into the turbine which permits a further increasing of the rotational speed of the engine without causing the charge pressure to rise to impermissibly high values. The problem of the coordination of several actuators with respect to one another therefore does not exist. The actuator may, for example, be a conventional pneumatic pressure element which is controlled by the pressure existing between the compressor and the internal-combustion engine. The integration of an adjustable turbine geometry and the blow-off device inside the turbine casing permits a compact construction and a secure actuation, first, of the guide blades in a first area and, following that, of the blow-off device in a second area.